(1) Field of the Invention
The present invention relates generally to methods for rapidly making piezoelectric transducers using piezoelectric material. In one possible embodiment, the invention is directed to a method for building a transducer onto an inner form with a conductive surface.
(2) Description of the Prior Art
In the past, piezoelectric transducers have been produced using flat sheets of material that are cut into segments and adhesively bonded to a desired configuration.
The following U.S. patents describe various prior art transducer systems. However, as discussed below, transducers made by some of the following prior art methods may be unsuitable for use in underwater environments where pressures are encountered.
U.S. Pat. No. 4,787,126, issued Nov. 29, 1988, to Oliver, discloses a dark field ultrasonic transducer that is constructed with an outer annular spherical or conical transducer element and an inner spherical element. The outer annular element is excited and insonifies a small portion of a part surface near a discontinuity or crack with longitudinal waves or with surface waves. The inner dark field element is not focused to be sensitive to either reflected sound or waves reradiated from the surface waves, but detects sound scattered from surface discontinuities such as a crack edge. When surface waves strike a crack edge and restrikes it after reflection from the bottom of the crack, two pulses are received and the time delay between them is a measure of crack depth. The crack shape and crack depth profile are determined as the part is scanned. A sphere-cone transducer, the preferred embodiment, is fabricated by stretching thin piezoelectric polymer film over a tool having a ball embedded in a conical surface.
U.S. Pat. No. 5,825,902, issued Oct. 20, 1998, to Fujishima, discloses a spherical piezoelectric speaker having a small and simple structure, a wide sound frequency range and a high sound pressure includes a spherical shell piezoelectric ceramic body which is hollow inside and an external electrode and an internal electrode defining a driving device for oscillating the spherical shell piezoelectric ceramic body. A sound absorber is provided in a hollow section of the piezoelectric ceramic body and a frame for holding the piezoelectric ceramic body is disposed on the outer surface of the piezoelectric ceramic body via dampers for reducing an influence of external oscillation.
U.S. Pat. No. 6,215,231, issued Apr. 10, 2001, to Newnham et al, discloses an electroactive device incorporating the invention that is conFIGUREd from an electroactive ceramic hollow sphere having an inner surface, an outer surface, a wall thickness aspect and a radius aspect. Conductive electrodes are positioned on opposed surfaces of said sphere and conductors enable application of an electrical potential between the conductive electrodes to enable a field to be applied to the sphere that causes a dimension change in the radius aspect and thickness aspect thereof.
U.S. Pat. No. 6,654,993, issued Dec. 2, 2003, to Zhang et al, discloses a process for fabricating a ceramic electroactive transducer of a predetermined shape. The process comprises the steps of providing a suitably shaped core having an outer surface, attaching a first conductor to the outer surface of the core, coating an inner conductive electrode on the outer surface of the core such that the inner conductive electrode is in electrical communication with the first conductor, coating a ceramic layer onto the inner electrode, thereafter sintering the ceramic layer, coating an outer electrode onto the sintered ceramic layer to produce an outer electrode that is not in electrical communication with the first conductor, and then poling the sintered ceramic layer across the inner electrode and the outer electrode to produce the ceramic electrode.
U.S. Pat. No. 7,019,445, issued Mar. 28, 2006, to Zhang et al, discloses a′process for fabricating a ceramic electroactive transducer of a predetermined shape. The process comprises the steps of providing a suitably shaped core having an outer surface, attaching a first conductor to the outer surface of the core, coating an inner conductive electrode on the outer surface of the core such that the inner conductive electrode is in electrical communication with the first conductor, coating a ceramic layer onto the inner electrode, thereafter sintering the ceramic layer, coating an outer electrode onto the sintered ceramic layer to produce an outer electrode that is not in electrical communication with the first conductor, and then poling the sintered ceramic layer across the inner electrode and the outer electrode to produce the ceramic electrode.
The above cited prior art does not disclose a transducer made utilizing a hollow metallic form. For example, Zhang et al., U.S. Pat. No. 6,654,993 and Zhang et al., U.S. Pat. No. 7,019,445 propose a spherical transducer made from a piezoelectric ceramic.
Moreover, the inner metallic coating used by Zhang is simply a metallic coating that is not sufficiently thick to be strong enough to provide support. Instead, Zhang utilizes ceramic as the structural material. Use in underwater environments where pressure is encountered is likely to be problematic and may crush, crack or deform the ceramic material of the Zhang transducer.
Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.